Conventional offshore support structures have deck legs that are vertical or are battered outward as they extend downwards. Various conventional arrangements provide sufficient structural support for the deck and offshore device but the associated dimensions of structures result in high material and installation expense. Wind turbines have conventionally been supported on mono-piles when placed offshore. Recently, there has been a drive to position wind turbines further from shore (approximately six to seven or more miles offshore), and in deeper water, in part to increase the aesthetics of the view from the shoreline. To support wind turbines in relatively deep water, mono-piles become extremely long, heavy, and cumbersome, making mono-piles relatively expensive as a wind turbine support.
Jacket type foundations or support structures with driven pipe piles have been used to support offshore wind turbines in recent years as the offshore wind industry has considered deeper water sites not previously considered feasible for mono-pile or gravity type foundations based on the added cost. As turbines grew in size to generate more power, the complexity and weight of a joint or transition piece, located between lower supports and the wind turbine tower, increased. This joint is typically a cast, forged, or heavy wall steel welded connection manufactured during the onshore fabrication phase of construction. The fabrication and installation of heavy wall joints can be a significant cost component to the wind turbine foundation.